1. Field of the Invention
The present invention relates to a cut design of ornamental diamonds and, more particularly, to a novel cut design of a diamond felt to be more beautiful by a person observing the diamond.
2. Description of the Related Art
In order to provide brilliant diamonds for use in ornaments by cutting, diamonds for ornamental use in the round brilliant cut having 58 facets and jewelry using such diamonds have been obtained.
Four criteria used in evaluating diamonds, commonly known as 4C's, are as follows:    1. Carat (unit of weight);    2. Color;    3. Cut (proportion, symmetry and polish); and    4. Clarity (quality and quantity of inclusions).
Regarding the weight expressed in carats, a diamond has traditionally been evaluated in size, which is measured in weight. The color depends on the raw gemstone; colorless and transparent stones are scarce and highly valued. The Gemological Institute of America (GIA) assigns D, E and F grades to colorless and transparent diamonds, and yellowish, if only slightly, ones are graded K or even lower. Cut design gives brilliancy and scintillation to a gem. The relative clarity is caused by inherent impurities and/or flaws of the raw gemstones.
Since the color and clarity are intrinsic to the gemstone, the only factor permitting artifice is the cut design, which determines brilliancy and scintillation. Therefore, studies have been continued to find cut designs that can enhance these attributes.
Mathematician Tolkowsky proposed what is known as the GIA system of cut design to increase the brilliancy of diamonds. The ideal cut according to the GIA system has a pavilion angle of 40.75 degrees, a crown angle of 34.50 degrees and a table diameter corresponding to 53% of the girdle diameter. Although a cut should be evaluated according to its contribution to beauty, more importance has been put on the yield from raw gemstone in determining a cut design of ornamental diamonds.
From the studies of the inventors about a cut design of ornamental diamonds for increasing brilliancy of the diamonds, the inventors proposed a cut design which permits simultaneous observation of lights coming into the diamond through crown facets and coming out from the crown facets, lights coming into the diamond through a table facet and out from the crown facets and lights coming into the diamond through the crown facets and out from the table facet, when a round brilliant cut diamond is observed from above the table facet of the diamond. To realize this feature, in the cut design, the pavilion angle (denoted as p hereafter) ranges from 45 degrees to 37.5 degrees and the crown angle (denoted as c hereafter) in degrees is within a range of satisfying the following equation:−3.5×p+163.6≧c≧−3.8333×p+174.232.The cut design was filed for patent as U.S. patent application Ser. No. 09/879,750 (filed Jun. 12, 2001). The center values of the pavilion angle (p) and the crown angle (c) are 38.5 degrees and 27.92 degrees, respectively.
The brilliancy of diamonds is a result of observer's perception on light which is reflected in a diamond after entering the diamond from the outside. The degree of brilliancy of a diamond is determined by the amount of light reflected from the diamond. The amount of light is ordinarily evaluated as a physical quantity of reflected light.
A result of human perception on brilliancy, however, is not determined by a physical quantity of reflected light alone. In order for a diamond to make an observer feel beautiful, the diamond must reflect a large amount of perceptible light, in the psycophysical meaning.
When an ornamental diamond is observed, light coming out through a table facet or crown facets of the diamond is perceived. If the amount of light coming out through a table facet or crown facets of a diamond is large, the diamond is evaluated as brilliant.
On the other hand, for a reason relating to working, a diamond which is cut in a round brilliant cut manner has, on the periphery of the boundary between the crown and the pavilion, a cylindrical surface or surfaces of a polygonal prism called a girdle. Ordinarily, the height (denoted as h hereafter) of the girdle is minimized. No study has been made about the relationship between the girdle height and the amount of reflected light.